Comparative Electrochemical Investigation of Pt, Au and Ti Electrodes on Liquid Crystal Polymer for the Application of Neuromuscular Prostheses

This paper studies the electrochemical impedance of Platinum (Pt), Gold (Au), and Titanium (Ti) deposited on liquid crystal polymer (LCP) to understand charge transfer mechanism of implantable electrodes for neuromuscular electrical stimulation. Electrodes are fabricated through e-beam evaporation and characterized using electrochemical impedance spectroscopy (EIS) and atomic force microscopy (AFM) measurements. A theoretical model is proposed to explain physical functionalities. The results demonstrate as the size of electrodes increases, higher conductivity and double layer capacitance are obtained. In neuromuscular stimulation frequencies, Pt electrodes offer the best conductivity followed by Ti and Au respectively. This material dependence of impedance magnitude is related to the surface morphology of the electrodes and is assessed by AFM. Deposition pressure dependence of Ti electrodes on the impedance is observed due to change of surface roughness and double layer capacitor. This study addresses the interface impedance of implanted electrodes and permits further development of neuromuscular prostheses.